TM 1-1520-238-10 2-42 Change 9 Section  V. FLIGHT CONTROL SYSTEM 2.37   FLIGHT CONTROL SYSTEM. The flight control system (fig 2-25) consists of hydrome- chanical  flight  controls,  augmented  by  digital  automatic stabilization equipment (DASE), and an automatically or manually  controlled  stabilator.  The  flight  control  system establishes  vertical,  longitudinal,  lateral,  and  directional flight of the helicopter. The flight controls provide a cyclic stick, collective stick, and directional pedals in each crew station, connected in tandem, to provide control inputs to the main and tail rotor hydraulic servo actuators. A mixing unit combines inputs from the servoactuators, and trans- mits them to a non-rotating swashplate. The swashplate changes the linear motion from the mixer unit to rotating motion.  The  swashplate  provides  pitch  changes  for  the four main rotor blades. Pedal inputs are transmitted in a similar manner to the tail rotor blades, except the mixer unit is not required. Description and operation of the main and tail rotor systems is in Section VIII. NOTE Helicopters  with  operable  BUCS  have shear pins installed in the SPADs in place of steel pins. They also have servos equipped for BUCS operation. Each mechanical flight control linkage has a shear pin actuated  decoupler  (SPAD)  installed.  The  SPADs  allow backup control system (BUCS) engagement by means of a microswitch inside each SPAD if a jam occurs in the me- chanical flight controls. The shear pins in the pilot SPADs shear at a force lower than those in the CPG SPADs. The SPADs are continuously monitored by the FD/LS. A single microswitch failure in one or more axes will cause a FD/LS message to appear. CAUTION · Do not move flight controls without hydraulic power. You may damage or shear pins in the SPADs. · Care  shall  be  exercised  in  extending or folding down the CPG cyclic stick when  the  rotors  are  turning.  Cyclic control system inputs may occur. It is recommended  that  the  pilot  hold  his cyclic  stick  steady  while  the  CPG  is extending or folding his cyclic stick. 2.37.1   Cyclic  Sticks. The  cyclic  sticks,  one  in  each crew station, provide for helicopter movement about the pitch and roll axes. The CPG stick has a lockpin release mechanism at the base of the stick. This allows the CPG to fold the stick down while viewing the heads-down dis- play  and  provides  greater  ease  for  ingress/egress.  The cyclic stick remains functional in this position and is re- turned to the extended position by pulling aft on a lever in front of the stick grip. Both cyclic stick grips (fig 2-26) have switches for weapons firing, DASE disengagement, trim feel,  radio  and  intercommunications,  and  flight  modes symbology. The pilot grip also has a remote transmitter selector switch for radio selection. These switches will be described in more detail with their associated systems. 2.37.2   Collective Sticks. The collective sticks in both crew stations (fig 2-26) provide the crew with a means of adjusting pitch angle of the main rotor blades and fuel flow metering requirements of the gas generator turbine. Each collective stick has an engine chop collar just aft of the col- lective stick switch box (see Section III) to permit both en- gines to be reduced to idle without moving the PWR lev- ers.  A  switch  panel  at  the  end  of  each  collective  stick contains a searchlight (SRCH LT) switch, an extend-re- tract  (EXT-RET)  momentary  searchlight  switch,  a  wing stores jettison guarded button (ST JTSN), a NVS switch, a BRSIT HMD/PLRT switch, and a radio frequency over- ride (RF OVRD) switch. The RF OVRD switch is nonfunc- tional. Both collective sticks have a BUCS select trigger switch.  The  switch  in  the  Pilot  station  is  non  functional. The switch in the CPG station is utilized to select BUCS. These switches will be discussed in more detail with their respective  systems.  A  twist-type  friction  adjustment  is installed on the collective assembly to prevent the collec- tive stick from creeping during flight. 2.37.3   Directional  Control  Pedals. The  directional control pedals, one set in each crew station, provide for helicopter  movement  about  the  yaw  axis.  Both  sets  of pedals are adjusted by applying foot pressure and moving a  pedal  adjust  quick-release  lever.  Pressing  the  upper portion of either pedal actuates a master brake cylinder which delivers hydraulic power to a brake disc at the re- spective main landing gear wheel. Section I contains de- scriptions of the main landing gear and brake system.